TILLAGE AND TRAFFIC INFLUENCES ON WATER AND SOLUTE TRANSPORT IN CORN-SOYBEAN SYSTEMS

Tillage management may influence water and solute movement throughout the root zone. To evaluate tillage effects on solute transport, parame ters were estimated from breakthrough curves and directly measured mac ropores in no-till (NT) and moldboard-plowing (MBD) systems with traff ic control on a Nicollet clay loam (fine-loamy, mixed, mesic Aquic Hap ludoll) and a Rozetta silt loam (fine-silty, mixed, mesic Typic Haplud alf). Ridge tillage recently imposed on long-term NT (RT/NT) was compa red with chisel tillage (CHT) on a Seaton silt loam (fine-silty, mixed , mesic Typic Hapludalf) where manure was injected without traffic con trol. Breakthrough curves (Br- tracer) were measured in undisturbed so il cores from the Ap horizon (0-250 mm) and adjacent subsoil (250-500 mm) and were fitted to a physical, nonequilibrium two-domain model to estimate mean pore-water velocity of the mobile domain (V-m) and the f raction of water (v) participating in Br- transport. The V-m ranged fr om 0.10 to 10 mm s(-1), while v ranged from 0.02 to 0.50. Means did no t differ between the Nicollet and Rozetta soils in 1988, yet significa nt tillage X horizon interactions indicated more solute bypass in NT t han in MBD. R-lore macropores and a larger macropore conductivity (K-m ) were observed in NT than in MBD. Greater V-m and smaller v occurred (P < 0.05) in CHT than in RT/NT because RT/NT lacked secondary cultiva tion to remove compaction from manure injection. Traffic control in NT on the Nicollet and Rozetta soils produced high V-m and low v compare d with RT/NT on the Seaton soil. Both V-m and v can be estimated from the more easily measured K-m.